Endoscopic surgical instruments are often preferred over traditional open surgical devices since a smaller incision tends to reduce the post-operative recovery time and complications. Consequently, significant development has gone into a range of endoscopic surgical instruments that are suitable for precise placement of a distal end effector at a desired surgical site through a cannula of a trocar. These distal end effectors engage the tissue in a number of ways to achieve a diagnostic or therapeutic effect (e.g., endocutter, grasper, cutter, staplers, clip applier, access device, drug/gene therapy delivery device, and energy device using ultrasound, RF, laser, etc.).
Known surgical staplers include an end effector that can articulate relative to the staple shaft, and that can be actuated to apply staples to tissue. Some linear end effectors simultaneously make a longitudinal incision in tissue and apply lines of staples on opposing sides of the incision. The end effector includes a pair of cooperating jaw members that, if the instrument is intended for endoscopic or laparoscopic applications, are capable of passing through a cannula passageway. One of the jaw members receives a staple cartridge having at least two laterally spaced rows of staples. The other jaw member defines an anvil having staple-forming pockets aligned with the rows of staples in the cartridge. Some current staplers also use reciprocating wedges which, when driven distally, pass through openings in the staple cartridge and engage drivers supporting the staples to effect the firing of the staples toward the anvil.
One drawback to current stapling devices is that a large force is required to effect articulation and actuation, and the force changes throughout the course of the firing stroke. Most current stapling devices utilize one or more hand-squeezed triggers. During articulation, the load is low when the end effector is close to linearly aligned with the shaft, and it increases as the end effector is articulated. During actuation, the load is low during early portions of the stroke when the staples are advancing out of the cartridge and piercing the tissue. Once the staples enter into the anvil pockets, the resistance and load rises rapidly as the staple legs buckle. Then the resistance and load drop down and rise again as the staples are formed. In contrast, the operator has maximum effective strength at the early and mid-stages of the firing stroke, whereas the effective strength is minimized during the final stages of closure. The large force necessary to effect articulation and actuation, as well as the variations in the force, can often exceed the surgeon's hand strength and could potentially result in binding or other malfunctions that may occur when an unexpectedly higher force is required.
The large force required to effect firing can also interfere with the flexibility or adjustability of the shaft. Currently, the end effector can be pivotally coupled to the shaft, or the shaft can be flexible to allow the shaft to travel through a curved pathway. The transfer of force from the handle to the end effector can necessarily interfere with the pivoted or curved orientation of the shaft, potentially causing it to straighten.
Accordingly, there remains a need for methods and devices for actuating and/or articulating a surgical stapler, and in particular for methods and devices that require a low force to effect actuation and/or articulation of a surgical stapler.